A post-Brexit hard border will have to be policed either with cameras or “boots on the ground”, a top Swiss official has suggested.

There is no other way, said lieutenant colonel Rebekka Straessle, chief of staff of the Swiss Border Guard.

The Swiss/EU border operates as it does with cameras on crossing points backed up by an intelligence process, Lt Col Straessle told Westminster’s Northern Ireland Affairs Committee.

The only alternative was “boots on the ground”, she said. Lt Col Straessle said there are cameras on most of the border crossings, filming licence plates.

“You have either people on the ground, boots on the ground, or you have technical means,” the senior official said, responding to a question about whether it was possible to have a border without physical infrastructure.

The British government has stressed that it does not want any physical infrastructure on the Irish border, and claims it wants to maintain it “broadly as it is now”. UK chancellor Philip Hammond warned MPs last month that cameras and other infrastructure would be deemed a “legitimate target”.

He said any physical aspects put in place to control the crossing would be seen as an affront to “those who do not recognise” the border on this island.

But Col Straessle told MPs yesterday policing a border involved either cameras or manned checks: “I don’t see a third way. For us, it is preferable to have technical means and to have an intelligence process in the background.”

The head of Switzerland’s customs service, Dr Christian Bock, told the committee that mobile patrols also take place across the border region.

“When you say that you don’t want, from historical political reasons, nothing at the border, then you have to compensate,” said Dr Bock, director general of the Swiss Federal Customs Administration.

“Then you have to compensate in my view with mobile patrols. At the end of the day you need people performing checks.”

Dr Bock said he did believe a system could be designed for the border here that didn’t entail physical checkpoints.

But he said that would require “common patrols” between the UK and the Republic to find “irregularities”, as well as an intelligence process to back this up.

“You need control points, not at the border, but somewhere in the country,” Dr Bock said. “You need controls not at the border, but at the enterprises. You need a system of some sort of pre-qualification, like the Authorised Economic Operator, and then you need a system for low-risk trade, or when you have trade of the same kind of stuff.”

He said that for everyday goods, such as milk crossing the border, “you don’t need a system where you stop every time at the border”.Dr Bock also said German helicopters fly across the Swiss/German border, with staff from Switzerland on board.He said checks are taking place 100pc of the time through risk-based data checks. Physical checks take place between 1pc and 2pc of the time, he said.